1. Field of the Invention
The present invention relates to jet engine multiduct noise suppressors and particulary to a modification of such a suppressor for increasing its noise suppression effectiveness.
2. Prior Art
It is known that the noise of a jet engine exhaust can be suppressed to a considerable degree by utilization of a multiduct noise suppressor. The extent to which the noise of the jet exhaust is suppressed depends principally on the number of ducts utilized in such a suppressor. Consequently, a sufficient number of ducts must be used to approach the desired degree of noise reduction. If the suppressor includes too many ducts, however, or if the ducts are too small, the friction of the exhaust gas passing through the ducts will be higher than desirable, resulting in too great a sacrifice of engine power.
Where a multiduct noise suppressor is used for a jet engine, the residual noise is composed of two principal components. The first component is of relatively high pitch and occurs prior to merger of the jets issuing from the several ducts. The other component is of comparatively low pitch and is caused by that portion of the jet exhaust rearward of the location where the jets from the several ducts merge. For subsonic aircraft it has been found that the premerged exhaust jet noise usually is more annoying and objectionable than the postmerged jet noise.
The principal problem in suppressing the noise of a jet engine exhaust is to effect such suppression to a noise level and type that is considered to be tolerable with minimal loss of power and increase of drag and by utilization of a suppressor structure that is reasonably light.
A representative multiduct noise suppressor is disclosed in U.S. Pat. No. 3,612,212 in which the ducts are in the form of tubes. The array of such tubes differs from that of the noise suppressor of the present invention in that the tubes project to different locations rearward as shown in FIG. 1 of that patent. In FIGS. 6, 7 and 8 of U.S. Pat. No. 3,612,212, side nozzles are directed inward, but the major portion of the exhuast is discharged in parallel jets through three discharge tubes arranged in a vertical row.
U.S. Pat. No. 2,990,905 shows a jet exhaust noise suppressor in which an annular row of small convergent nozzles is arranged around a much larger main jet nozzle.
In U.S. Pat. No. 2,935,842 exhaust ducts are in the form of concentric slots instead of being generally cylindrical.
Canadian Pat. No. 618,154 shows a multiduct noise suppressor which reduces postmerged jet engine exhaust noise.